Electronic carrier devices and methods of manufacture

ABSTRACT

New chip carrier type devices have a substrate with a particle-loaded ink defining a plurality of distinct circuit paths. The circuit paths carry a conductive metal plating. The ink is designed with binder and adhesive means which are used to firmly attach the ink to the substrate which can be an organic resin.

This is a continuation of application Ser. No. 664,598, filed Oct. 25,1984, now abandoned.

BACKGROUND OF THE INVENTION

Integrated circuit chip carriers are widely used in the industry. Thechip carriers provide a means for mounting integrated circuitry to thecircuitry of a circuit board to which the chip carriers are attached.

The most widely used chip carriers in the industry are made of ceramicbases on which electrically conductive circuit paths are formed. Thepathways are often formed by the use of deposited metal particles in anorganic polymer binder treated by firing to high temperatures as over200° C. to remove the organic binder.

Developments in providing chip carriers are found in a variety of U.S.patents including the following U.S. Pat. Nos.: 4,366,342; 3,942,245;3,483,308; 3,729,819; and 3,434,877. Patents of interest in the fieldfurther include: U.S. Pat. Nos. 3,909,838; 3,942,245; 3,975,757;4,079,511; 4,147,889; 4,278,991; 4,366,342; 3,930,115; 3,936,866;4,180,828; 4,220,917; 4,221,047; 4,339,621; 4,387,388; 4,398,208 and2,959,498.

U.S. Pat. No. 4,147,889 discloses a chip carrier which includes a moldeddielectric base of an organic resin in the form of a tray for receivinga chip. Conductive electric circuit paths of traces are separatelymounted in the tray. However, the circuit paths are suggested to beformed by techniques known in the art with a specific statement thatlaminating and etching can be used. Subsequent to plating the patentsuggests deforming the carrier into a dish configuration. Thus, theformation of the chip carrier is carried out in one form with subsequentforming to a three-dimensional form.

SUMMARY OF THE INVENTION

It is an object of this invention to provide improved three-dimensionaldevices comprising an insulated substrate and having electricallyconductive paths thereon which devices can be rapidly formed in highspeed production with accurate precise pathway arrangement having goodresolution and good electrical conductivity.

Another object of this invention is to provide devices in accordancewith the preceding object which are formed of electrically insulatingorganic resins and are particularly suitable for use as integratedcircuit chip carriers.

Another object of this invention is to provide a device in accordancewith the preceding objects which is highly resistant to thermal cyclingdue to the closeness of thermal coefficient of expansion between thethree-dimensional device substrate and the substrate of a circuit boardon which the device is mounted.

A still further object of this invention is to provide an improvedmethod of forming a three-dimensional device in accordance with thepreceding objects, which method is particularly suitable for use andprinting in a three-dimensional form at high speed with good resolution.

Still another object of this invention is to provide a cost effectivehigh speed manufacturing method in accordance with the preceding methodwhich is particularly suitable for use in forming integrated circuitchip carriers.

According to the invention, a preferred three-dimensional devicecomprises an electrically insulation substrate, preferably of an organicresin, having a thickness and defining a first side surface having anelectronic component mounting area, a flange extending at an angle fromthe mounting area and defining a lip area having an outer peripheraledge. A particle-loaded ink lies in a plurality of distinct circuitpaths and extends from the vicinity of said mounting are toward saidlip. The particle-loaded ink is bound to said substrate by athermosetting resin and a conductive metal plating overlies the ink andprovides high electrical conductivity to said circuit paths. When thesubstrate is an organic resin it has a coefficient of thermal expansionpredetermined to match with that of common organic resin circuit boardsubstrates so as to prevent delamination of said ink at expected thermalcycles encountered when chip carriers are mounted on the circuit boards.

Preferably the ink has a binder of a thermosetting resin and is appliedover a thermosetting adhesive which aids in bonding the ink to theorganic resin or plastic substrate. Preferably the particles in the inkare electrically-conductive metals but always are particles whichcontain a metal component and which permit good plating with highresolution. The plating is preferably a metal applied by electrolessplating without activation, although in the case of certain inksactivation may be needed.

Preferably the ink when printed on the chip carrier substrates passesthe Plateability Standard Test and the completed products pass theTensile Pull Strength Test as described in this specification.

According to the method of this invention a three-dimensional devicesuch as a chip carrier is formed preferably on a resin substrate havinga thickness and defining a first side surface having an electroniccomponent mounting area, a flange extending at an angle from themounting area and defining a lip area having an outer peripheral edge.The method comprises providing the device in a preformedthree-dimensional configuration which is preferably injection-molded. Aresilient compressible printing means and preferably a silicone pad isused to apply the printing ink to the three-dimensional surface of thesubstrate in a plurality of electrically conductive circuit paths ortraces in a three-dimensional array with the ink having a thermosettingbinder. The ink is adhered to the device and the paths are plated withan electrically conductive coating

Preferably the plating is carried out by electroless plating techniques.The pad printer can be any resilient printing means although a siliconerubber pad is preferred. In the preferred arrangement, the ink ispositioned onto a carrier flat base which is preferably a gravureink-holding depression, which is struck by the resilient pad to pick upthe ink and the ink transferred to the substrate to permit curing on thesubstrate. In the most preferred form, a curable binder of a thermosetorganic material is first applied to the substrate before printing withthe ink.

In one form of the invention the printing ink is formed of Fe₂ Pparticles in a binder. Although the ink layer is not itself electricallyconductive it forms an excellent base after activation with palladiumchloride for plating of conductive nickel.

It is a feature of this invention that conventional printing apparatussuch as Tampoflex printers produced by Tampoflex GmbH of Stuttgart,Germany and Inkflex by Ink Applications Corp. of Wilmington, Mass. canbe used for the printing operation. High speeds can be carried out whilestill obtaining good resolution of electrically conductive traces withgood electrical separation and excellent adhesion to the base orsubstrate. Matched coefficients of thermal expansion in the chip carriersubstrate and circuit board base permit overcoming problems that canarise when using conventional ceramic devices due to the differential incoefficient of thermal expansion between ceramics and plastic printedcircuit baseboards. The devices are tough and easily handled inautomatic processing machines.

DESCRIPTION OF THE DRAWINGS

The above and other features, objects and advantages of the presentinvention will be better understood from a reading of the followingspecification in conjunction with the accompanying drawings in which:

FIG. 1 is a top plan view of an electronic chip carrier in accordancewith the preferred embodiment of this invention;

FIG. 2 is a cross sectional view through line 2--2 thereof with thelayers of adhesive and ink exaggerated for clarity;

FIG. 3 is a semidiagrammatic cross-sectional view through a chip carrierin accordance with FIG. 1 mounted on a circuit board;

FIG. 4 is a block diagram showing of a preferred method in accordancewith the method of this invention; and

FIGS. 5A and 5B are semidiagrammatic showings of the ink transferprocess of the preferred embodiment of the method of this invention.

BRIEF DESCRIPTION OF PREFERRED EMBODIMENTS

With reference now to the drawings, the preferred embodiment of a chipcarrier in accordance with this invention is illustrated at 10 in FIGS.1 through 3. The chip carrier 10 is of conventional design except thatit is preferably formed of an organic resin substrate 11 rather than themore-conventional ceramic. The upper surface of the substrate 11 has afirst side which carries a curable thermosetting adhesive layer 12 and aparticle-loaded ink layer 13 which is platable to carry a plating 14which is electrically conductive. The ink can also be a conductivelayer.

The substrate and chip carrier are in three-dimensional configurationproviding an upwardly extending flange 15 extending about a mountingarea or surface 16 at an angle to the substantially planar mounting area16. The angle can vary as known in the art. An upper lip 17 provides anupper surface 18 which can be placed against electrical paths of aprinted circuit board to which the chip is to be mounted in accordancewith conventional practice. Preferably an outer peripheral lip edge 19is provided at an angle to the upper surface 18 which permits formationof an electrically-conductive path lying in a plane at an angle to theflat plane of surface 18. This angle is particularly useful when reflowsoldering the chip carriers to boards as will be described. The carriershown in FIG. 2 is injection-molded and includes a flat botton 30,angled rim 31 and a surrounding outer flat border 32 forming the bottomof flange 15. Flange 15 has a mounting area wall rim 43. Thisconfiguration can vary greatly depending on the particular applicationof the chip carrier or other device.

An electrical component is diagrammatically illustrated at 20 and hasleads diagrammatically illustrated at 21 attached to individual ones ofthe circuit paths or traces formed by the plating and ink 13, 14. Aplurality of leads can come from the integrated circuit to the vastplurality of traces such as 14.

The particular number of traces can vary greatly. In many cases whereprinted circuits are used many leads are used which must be electricallyconnected to discrete circuit traces in an extremely small area. Forthat reason, it is important to have good resolution with electricalisolation of one trace from another. This can be difficult whereprinting inks are used to form the traces. The particular method of thisinvention is particularly useful to provide desired electricalisolation.

Using the methods of this invention, good resolution can be obtained ifelectrical paths are printed substrates parallel to each other and0.008" apart.

FIG. 3 shows a conventional attachment of the chip carrier of thisinvention 10 to a printed circuit board 50 which can be of conventionaldesign. The traces with their plating 14 are placed on the circuit paths51 of the board 50 and soldered thereto by conventional means such asreflow soldering.

Note the solder filet 33 formed because of the plating over peripheraledge 19. This provides for better bonding and electrical continuitybetween the circuit paths of the chip carrier and those of the board.

The chip carriers of the present invention are dimensioned in accordancewith any of the known configurations for chip carriers normally formedwith ceramic substrates. For example, chip carriers fitting withindimensions of 0.4"×4" square to 2.5"×2.5" square are common. Althoughsquares are common, rectangular and other shapes can be used and in somecases, the three-dimensional devices can be used for other purposes thanchip carriers. In the conventional chip carrier, the flanges 15 extendupwardly at angles of from 20° to 60° with the top surfaces 18substantially parallel to the mounting surface 16 although this is notrequired. The lip 17 can have a mounting surface which is rounded incross section or in other configurations.

The baseboard or structural component of the chip carriers can be anydimensionally stable organic resin or plastic material and for examplethose known in the art. Such materials for the substrate include epoxymaterials such as glass filled G-10 and FR4, phenolic materials,polysulfones such as Udel brand and polyamide ether such as Ultem brand,polyethylne terephthalate (Rynite) of Dupont DeNemours of Wilmington,Del., polyarylether, polyarylate and polyarylsulphide. In someapplications the three-dimensional base can be of other materials suchas glass or metal providing an insulating layer is provided, such asmetal oxide, where metal bases are used so as to always have aninsulting surface onto which the circuit materials of this invention arepositioned.

The substrate can be thermosetting or thermoplastic of mixtures of thetwo. Preferably the substrates are resistant to temperatures normallyencountered in assembly and use of the device as chip carriers namelytemperatures in the range of from 50° C. to 260° C. and havethermal-coefficient of expansions in the range of from 1.1×10⁻⁵ to3.9×10⁻⁵ per °C. Preferably the moisture absorption at saturation is0.05% weight percent or less and more preferably 0.02% or less (usingASTM D570).

The substrate is normally used in thicknesses of from 0.04 to 0.10 inchalthough this can vary greatly depending upon the particular usage. Thesubstrate base is preferably substantially rigid. In some cases heatsink areas on the mounting surface 16 can be used in accordance withknown prior art practices.

The adhesive layer 12 is preferably a reactive resin and preferably acurable cross-linkable, thermosetting organic resin.

The adhesive may be any one or more of the many thermosettable resinsknown as adhesives or combinations of such resins with seeminglythermoplastic resins which are reactive sufficiently with the binderportion of the circuit element film and/or with another reactive resinwith which it is blended so as to forma cured thermoset interfacialbonding layer between the adherend (the dielectric surface) and theother adherend (the ink circuit element film). The theories underlyingadhesion are well developed, see e.g., Skiest, Handbook of Adhesives,2nd Edition, 1977, pp. 11-16, published by Van Nostrand ReinholdCompany, New York, N.Y., U.S.A. A wide variety of adhesive materials isemployable in the practice of this invention. Without intending to belimited, a preferred adhesive combination is the mixture of an acetalresin, viz. polyvinyl acetal, and an epoxy resin, as generally describedby Skiest, supra, pp. 507-527. Particularly good results are obtainedfrom a blend of polyvinylbutyral or polyvinylacetal and an epoxysubstituted novolak as described below. Other desirable adhesivesinclude thermoplastic polyester polyurethanes crosslinked bypolyfunctional blocked isocyanates whereby crosslinking is achieved bybinret and/or allophanate linkages. Straight epoxy systems are desirablesuch as the cycloaliphatic epoxides blended with polyols such aspolycaprolactone polyols. Where interreaction is achievable bycatalysis, a catalyst is supplied. Many resin systems are crosslinked toa cured condition using heat alone. Where the dielectric surface of thechip carrier is pre-preg, then the resin used in forming the finalcomposite of the dielectric surface may also be used as the adhesivelayer or interface. The options in respect to adhesives are many andvaried. Many additives may be incorporated into an adhesive formulationas known in the art.

The adhesive is preferably printable by pad printer although it can beapplied by any means. In some cases the adhesive layer overlies theentire surface about the flange and lip and peripheral edge since it isless expensive in some cases to apply the adhesive in that manner.However, it is also possible to apply the adhesive by a pad printingtechnique where only portions underlying the electrically conductivetraces 13 are applied after which the traces 13 are printed over theadhesive layer. Normally the adhesive is used in a thickness of from0.0001 to 0.0004 inch dry.

The printing ink layer 13 is of necessity a printing ink carrying metalcomponent-containing particles which provides for good platability. Theprinting ink can have high electrically-conductive properties althoughsuch properties are not absolutely required where plating is carriedout. In the preferred embodiment the metal component is anelectrically-conductive metal.

Suitable inks include particle-filled inks having as binders curable,thermosetting materials with reactive groups capable of reacting withthe adhesive layer. Such binders include thermosetting resins such asepoxy, epoxy novolac or glycerol ether bis-phenol A, phenolic, melamine,polyisocynate, polymamide, polyimide, acrylic, urea formaldehyde,polyester and cross linked or reactive urethane systems.

Especially preferably binders include phenol blocked isocyanates reactedwith novolac epoxides alone or blended with polyvinyl acetals, e.g.,polyvinyl butyral or polyvinyl formal resins. The blocked isocyanatesmay be deleted from such resin if desired.

The particles and binder are mixed together in a high boiling solventpreferably with slow evaporation characteristics to form a slurry (theink). Suitable solvents include cellosolve acetate, n-butyl carbitol,n-methyl-2-pyrolidine, N, N-dimentyl formamide, dimethyl sulfoxide,ethylene glycol, anisole, decaline, diethylene glycol diethyl ether,aniline, diethylene glycol dibutyl ether, diethylene glycol diemthylether, glycerol, tetralin, xylene, ethylene glycol monoethyl ether,chlorobenzene, diethyl carbonate, butyl acetate, ethylene glycolmonomethyl ether, toluene and the like. The solvent is vaporized duringthe curing rocess. The amount of resin in the ink on a dry basis is fromabout 46 to about 13 preferably from about 32 to about 13 percent of thevolume fraction.

The particles are metal component containing and preferablymetal-containing and are loaded in the ink in high amounts in the rangeof from 54 to 87 and preferably 68 to 87 percent of volume fractionbased on the volume of the dry film where metal-containing particles areused. Suitable inks include those with electrically conductive metal. Inone embodiment, precious or noble metals such as silver, gold, platinum,palladium, rhodium and ruthenium particles are used. The metal particlesmay comprise at least one of the metals from groups 5b, 6b, 7b, 8, 1b,2b and 3b of the periodic table of elements. Mixtures of particles canbe used such as mixtures of silver, gold and/or palladium with theremainder being particles of other metals or solids such as nickel,copper, zinc, aluminum, gallium, glass, metal oxides and nonmetal oxidesolids such as silica, mica and the like. In some cases metal coatedceramic particles such as metal coated glass or silica particles can beused. The precious metal, when used, preferably comprise at least 15% byweight up to 100% by weight of the particles in the composition and mostpreferably 20% by weight. Most preferably, the precious metals compriseat least 20% by weight of the particles in the ink composition. In onepreferred embodiment, the precious metal is silver in the form of flakesor platlets or rods allowing for maximum contact within the thermosetresin layer binder. The shape of the particle components is not narrowlycritical so long as it allows adequate silver to silver contact in thelayer to provide the level of electrical conductance where electricalconductance is sought in the ink rather than obtained solely through theuse of a conductive plating. When silver is used, silver flake can beused with metal particles such as nickel or tin. A particularlydesirable combination is 25% to 50% by weight of silver particles and75% to 50% by weight of nickel particles based on the particulatecontent only. Another preferred composition is one where the metalcontaining ink particles are nickel particles. The nickel particles canbe for example 3 to 5 micron particles of equi axis shape. The nickelparticles can be ball milled to platelet shape with aspect ratio of from5 to 20 to 1 to 20. The nickel particles do not provide high electricalconductivity to the ink but do provide for good plating.

Still another preferred embodiment for the particles of the ink comprisethe use of ferric phosphorus such as ferrophoS a trademark product ofHooker Chemical Company. Ferric phosphorus has substantially littleelectrical conductivity as an ink in accordance with the invention butis highly printable with good resolution and little or no smearing evenwhen printed in traces close together, as for example, 8 mil apart. Theferric phosphorus is platable but must be activated with palladiumchloride solutions to the allow electroless plating and thus is not asdesirable as use of nickel or silver-nickel or other particle containingink combinations which do not require activation for electrolessplating. Particle sizes of metal component particles in inks of thisinvention can vary greatly. Fe₂ P can vary from 3 to 22 microns inaverage particle size. Nickel particles can vary from 2 to 40 microns.Preferably the particles pass a 100 mesh size screen U.S. Sieve Standardand most preferably pass a 200 mesh size screen and are retained on a350 mesh size screen U.S. Standard.

The metal component-containing particle and binder of the ink are mixedtogether in a high boiling solvent to form a slurry which is in effectthe ink. Suitable solvents are known in the art as previously described.

The solvent is vaporized during the curing process. The amount of resinin the ink on a dry basis can be from about 2 to about 7 and preferablyfrom about 4% to about 6% by weight.

The metal component particle is preferably present in the slurry inamounts of from at least 93 to about 98% by weight on 100% solids basis.When electrical conductivity is to be obtained from the metal, it ispreferred to use preferably from 93% to 98% to achieve a desired levelof conductivity as for example a surface resistivity of below 0.5ohms/square and preferably from 0.1 to 0.005 ohms/square. Expressed inanother way, the metal component particles preferably should be fromabout 54% to about 87% by volume of the volume fraction based on thevolume of the dry film.

Preferably the inks of this invention which are metal particle carryinginks are designed so that the dried inks pass the Plateability StandardTest as defined below and chip carriers carrying the inks all pass theTensile Pull Strength Test. These tests are described below.

PLATEABILITY STANDARD TEST

This test defines the criteria by which the capability to apply, adhereand maintain adhesion of electroless nickel plating to the printed inkis determined.

(Note: This is not a plating standard test which would define quality,quantity, and process control related yield values. In addition, thistest only has significance with respect to chip carriers or devices inwhich metal particle containing inks are used and is not relied on withrespect to devices formed with Fe₂ P inks.)

In the Plateability Standard Test, a plastic chip carrier substrate,having additive lines each distinct physically and electricallyseparated from each other, is prepared for the electroless platingprocess using Enthone Ni 418 (manufactured by Enthone, Inc., WestHartford, Conn., U.S.A.) at 88° C. for 45 minutes. The carrier is asshown in FIG. 1 and has a 0.72×0.72 inch size and carries printedcircuit lines of this invention in a pattern of 64 radiating linesapproximately 0.3 inch in length, having a line width of 0.012 inch to0.025 inch.

A value satisfying the Plateability Standard Test is defined inclusivelyas:

1. 100% coverage of any distinct line which accepts the plating, (asdetermined by a 10×magnification visual examination).

2. no less than 95% of the lines must accept plating.

In addition to passing the test values above, the most preferredproducts of this invention have the following features:

1. Substantially all lines that accept plating are free of blisters andcracks (as determined by 10× magnification visual inspection), and

2. Substantially all lines that accept plating adhere and maintain theplating as determined by an adhesion peel test per I.P.C. Test MethodsManual Method Number 2.4.1., in which no plating may separate from theprinted circuit interface. This test is performed both before and aftersubmission to a salt spray environment per ASTM B-117 (5% neutral saltspray at 95° F. for 72 hours).

In addition both the metal particle inks above and the Fe₂ P type inksbelow pass the pull strength test described below:

Tensile Pull Strength Test

With respect to the pull strength of the circuit element, i.e., thesoldered interface to a printed circuit board, (as shown in FIG. 3) itshould be a minimum value of 150 p.s.i. (pounds per square inch) tensilepull for the plated circuit element in order to satisfy the requirementsof pull strength for this test. In this regard, the test is not the peelstrength test, see Coombs, supra, page 19-23, but a test similar to it.This procedure measures the tensile strength of the bond of a Ni platedcircuit element (as described in the plateability section herein) andmeasures ultimately either adhesive or cohesive failure of thecomposite.

The specimen is identical to the plateability standard having theconfiguration of FIG. 3. The carrier is soldered to a conventionalsubstractive process aminated copper epoxy glass circuit boardinterfacing at 64 locations, each having a solder contact area of 0.020inch by about 0.050 inch. The solder is Sn60 or SN62 containing fluxtype RA or RMA.

The specimen is mounted in a tensile (pull) test machine such that atensile load is applied through the center of the carrier. The testmachine (Instron model 1130 made by Instron Corp. of Canton, Mass.) hasa constant velocity capability of 1 inch/minute ±2% pull and a forcecapability of 100 lbs. full scale, and 10 lbs. full scale, with a forcesensitivity of ±1% of full scale. A chart recorder of similarsensitivity shall be used for data acquisition.

The recorder is calibrated to zero and then start the pull at 1inch/minute. Record the force at failure. The force (lbs.) is divided bya factor of 0.064 to determine the tensile strength in p.s.i.

The plated layer 14 is an electrically conductive layer that can be ofany metal. The plating is preferably carried out by electroless platingwith nickel being an ideally suitable plating material. Platingthicknesses of from 0.003 to 0.0008 inch and more can be used. Above0.0016 inch for plating becomes commercially undesirable. An electrolessnickel plating solution such as Enthone Ni418 manufactured by Enthone,Inc. of West Hartford, Conn. is a particularly-suitable electrolessnickel coating solution. Plating rates of 0.0004 to 0.0005 inch per hourcan be easily attained. Plating can be carried out for periods of from25 to 90 minutes or more of temperatures of from about 83° C. to about88° C.

Electroless plating in well-known in the art as, for example describedin PLATING, October 1959, "An Outline of the Chemistry Involved in theProcess of Catalytic Nickel Deposition from Aqueous Solutions", G.Gutzeit.

In some embodiments, the materials can be activated prior to plating asin the case of Fe₂ P wherein palladium chloride activation is used.Other electroless plating layers that have good electrical conductivitycan also be used. For example nickel, copper or gold plating can be usedfor layer 14. In some cases two platings can be used to improve wirebonding as, for example, gold plated over an electroless nickel layer.

It has been found that wire bond techniques for connecting electricalcomponents to the chip carriers can be used. However, the integrity andbond characteristics are enhanced if the chip carrier printed ink linesare first treated in accordance with this invention to compress the inkbefore plating. The compression step can be carried out in a suitabledie. The substrate which can be injection or compression molded and canhave traces of ink thereon is placed in a form and a press brought downto provide flat surfaces compressing each ink trace at least at its areato be bonded to leads such as the inner perimeter of the traces.Pressures of from 500 to 2000 psi which are non-destructive to the inktraces for time periods of from 3 to 15 seconds at temperatures of from350° F. to 600° F. are preferably used. The times, temperatures andpressures can vary depending on the ink and substrate used.Non-destructive parameters are easily chosen. In a preferred embodiment,1800 psi for 10 seconds is applied at 475° F. This provides a flatter,better surface for bonding after the ink is later plated in accordancewith this invention. Wire bonding is then easily carried out with goodbond integrity and electrical conductivity.

The inks of this invention are preferably designed to have a viscosityin the range of from 70,000 to 410,000 cps, Brookfield Viscometerspindle 7, speed 2 at 29° C. so as to be transfer printable. The inkused before plating has a dry thickness of from 0.0005 inch to 0.0015inch while the plating thicknesses are from 0.002 to 0.005 inch orhigher and preferably about 0.004 inch. The adhesive layer preferablyhas a dry thickness of from 0.001 to 0.005 inch.

The completed products have electrical paths or traces (formed by theink having a conductive plating thereover) which are densely loaded onthe upper surface of the chip carrier. The plated traces can have widthsof from 0.0012 to 0.050 inch and be spaced from 0.020 to 0.100 inchapart. Preferably tensile pull strengths of at least 150 psi areobtained. The devices are resistant to thermal cycling at temperaturesof from 50° C. to 150° C. at a rate of one cycle per hour up to 100hours and more. The devices pass the Plateability Standard Test and theTensile Pull Strength Test when metal particle-containing inks are used.

Turning now to the method of this invention, the steps in the method arediagrammatically shown in FIGS. 4 and 5. Basically a chip carryingsubstrate in a three-dimensional form is provided. The method can becarried out on all substrates including ceramic substrates although inits preferred form, significant advantages are obtained when thesubstrate is an organic resin or plastic. The substrate is preformedinto a three-dimensional form such as the form of FIG. 1. When thesubstrate or base is thermoplastic it can be injection-molded orotherwise preformed. Thermoplastic substrates can be preformed usingstandard molding or forming techniques such as compression molding.Adhesive is printed by the use of a yieldable printing means of thisinvention.

In the preferred form, the printing means is a three-dimensional pad 60mounted on a moveable piston shaft. The ink is positioned in a desiredpattern, as by use of standard gravure techniques, on a carrier platesuch as 61, or otherwise formed on the carrier plate in the desiredelectric path configuration. That configuration can be as shown inFIG. 1. The three-dimensional pad such as 60 or other compressible meansis applied to the carrier surface 62 to pick up the electrical pathconfiguration formed by the ink as shown in FIG. 5A. The ink is thentransferred to an underlying preformed three-dimensional insulatingsubstrate of chip carrier type device and applied thereto. The pad isresiliently deformed to print the desired pattern on a three-dimensionalsurface as shown in FIG. 5B. Silicone rubber pads are particularlyuseful to carry out the transfer. Surprisingly, the highly-metalcomponent particle-carrying ink is transferred wih good resolution athigh speed in the process of this invention. Preferably, an adhesivelayer of a durable thermosetting resin is applied prior to the ink so asto provide a reactive adhesive interlock between the ink and theunderlying layer. The adhesive and ink binder are as describedpreviously, which permits interaction of the materials.

As shown in FIG. 4, the adhesive is first printed on the chip carriereither in the pattern in which the ink is to be applied thereover orthroughout the upper surface if that is simpler and faster. Preferablydrying is then carried out as, for example, for three to five minutes at200° F. to remove the solvent from the adhesive.

The ink is then printed with the printer pad 60 which picks up the inkfrom the carrier layer 61 as described above. Preferably a single hit ofthe pad is used although in some cases in order to provide sufficientink deposit, two or more hits of the pad to the three-dimensionalcarrier are carried out.

A second drying step is preferably used to remove the ink solvent atthree to five minutes at 200° F.

The dried printed ink traces are then preferably pressed as previouslydescribed to improve wire bonding characteristics of the final product.

After the pressing step curing is carried out to cure and interact theadhesive and ink to form the final bond between the substrate and theink. Depending upon the particular materials used, the time andtemperature can vary although times of from 20 to 40 and preferably 30minutes at from 360° F. to 392° F. and preferably 360° F. has been founddesirable.

In a next step, plating is carried out by conventional electrolessplaalting preferably of nickel, copper or gold to form an electricallyconductive layer as known in the art with the electrically conductivecircuit patterns or pathways having a surface resistivity of no morethan 0.05 ohms per square. Electroless metal plating is well-known inthe art. Metallic coatings are deposited on solid catalytic surfacesthrough a process of chemical reduction. No electric current isrequired. Under the right conditions positive ions (cations) are freedfrom solution and the reduced metal forms a unique metallurgicalmaterial, sometimes referred to as metallic glass because it has littlecrystalline structure. Uniform coatings are normally formed which arealmost free of pores in most cases. The platings are often corrosionresistant and can be heat treated when necessary to decreasebrittleness. It should be noted that where Fe₂ P is used, a conventionalactivation step is first used as known in the art prior to plating,although in the preferred embodiments where metal particle-containinginks are used, no activation is necessary.

After plating, in a final step, post-curing is preferably carried out asfor example at 20 to 40 minutes and preferably 30 minutes at 360° F. to392° F. to finalize the cross linking and interaction of the adhesiveand ink binder.

The chip carriers are then completed and integrated circuits can bemounted in accordance with conventional procedures.

The chip carrier to board assembly follows conventional procedures andcan use conventional production equipment. For example, 0.005" to 0.008"of Sn62 (RMA) solder paste can be applied to the circuit path traces ofa conventional printed circuit. The chip carrier of this invention isthen aligned with its traces aligned with those of the board to which itis to be joined with the carrier setting on the paste. Drying is carriedout and vapor phase soldering with, for example, 60 seconds at 215° C.reflow and 15 seconds at 90° C. dwell time use to complete theprocedure.

It should be understood that there are many variations in the processingof this invention. The key step is the use of a compressible transfermeans such as a silicone rubber pad 60 to pick up a conductive pathwaypattern fromaa carrier surface such as 62 or other means and transfer itto a three-dimensional insulated base to allow rapid production ofhighly-conductive, mechanically-strong electrically conductive paths inelectrical products such as chip carriers. The silicone rubber pad 62can be other resilient materials and/or in other forms such as asilicone rubber roller which is used to pick up and transfer thepattern.

While the pattern is preferably formed on a carrier surface such as 62by conventional gravure techniques, other methods can be used. Forexample the carrier surface can be a gravure plate with preformedpatterns in conventional gravure-type transfer with gravure rubberroller pads used in a rolling action. Similarly the pressing of thesurface in step 5B can be carried out by a roller action rather than asingle pad-like action. In all caess because a resilient transfer meansis used, three-dimensional printing can be carried out. Preferably theink used in suitable for gravure printing. Similarly the adhesive issuitably formulated with solvents so as to have a screenable viscositysuitable for printing or spraying, as desired.

The following examples serve to give specific illustrations of thepractice of this invention but are not intended in any way to act tolimit the scope of this invention.

Example 1.

A chip carrier such as 10 is formed of a substrate molded from a glassfilled polyethylene terephalate material such as Rynite 555 obtainedfrom DuPont Co. of Wilmington, Del., having tensile strength of 28,500p.s.i. (ASTM 638) heat deflection temperature (264 p.s.i.) of 445° F.(ASTM D648), a coefficient of linear thermal expansion of 1.3×10⁻⁵in/in/°F. (ASTM D696) and a moisture absorption (24 hours at 73° F.) of0.04% by weight (ASTM D570).

The substrate composition is molded at 300° C. in a cavity mold using ahydraulic press to form a three-dimensional chip carrier substrate asdescribed in the Plateability Standard Test where the thickness of thesubstrate varies in cross section from about 0.03 inch to 0.08 inch.

Separately, a two part adhesive containing the following ingredients isprepared:

Part A

(I) 11.41 parts by weight of an epoxy resin derived from epichlorohydrinand bisphenol A (Epon 1009F obtained from Shell Chemical Co.),

(II) 40.8 parts by weight of a saturated polyester having an averageequivalent weight of 260, a hydroxy content of 6.5%, a maximum acidnumber of 4.0, an approximate specific gravity of 1.12 at 25° C.(Desmophen 1100 obtained from Mobay Chemical Corporation, Pittsburgh,Pa.), and

(III) 0.068 parts by weight of a nonionic surfactant which is a liquidfluorinated alkyl ester (FC-430 obtained from 3M Corporation).

Part B

47.67 parts by weight of polytoluene diisocyanate, containing 6 to 7%free monomer (CB-60 obtained from Mobay Chemical Co.).

Parts A and B are then mixed together. A solvent containing isopropanoland methylethylketone (in a ratio of 3/2) is added to obtain a viscosityof 18 seconds Zhan cup No. 2 at 25° C.

The prepared adhesive is sprayed onto the treated chip carrier at auniform dry thickness of 0.002 inch. Then the adhesive coated substrateis placed in a convective oven at 200° F. for 5 minutes until theadhesive coat was dry but not fully cured.

A Tampaflex printer is then used. The carrier surface 62 has a patterncomprising a embodiment as shown FIG. 1 where ink lines are applied tothe three-dimensional surface with the conductive lines are as describedin the Plateability Standard Test.

The conductive pattern is formed by gravure technique on the surface 62and transferred as shown at FIGS. 5A, 5B at a printing pressure of about14.5 p.s.i. The ink used is formed by blending together at roomtemperature:

(I) 3 percent by weight of an epoxy novolak resin having an average of3.6 oxirane groupos per molecule, having a viscosity in the range of1100 to 1700 centipoise (at 52° C.). Its epoxy equivalent was in therange of 172 to 179. The average value of repeat units was 0.2,(D.E.N.431-obtained from Dow Chemical Co., Midland, Mich., and

(II) 2 percent by weight of poly(vinyl formal) resin having a molecularweight of 10,000 to 15,000 and a solution viscosity of 100 to 200centipoise (measured as 15% by weight in a 4:2 solution of dibasicester¹ : (an ester mixture of 23 weight percent dimethyl succinate, 56%dimethyl glutarate, and 21 weight percent dimethyl adipate.) N-methylpyrrolidine at 25° C.). Formvar 5/59 is obtained from Monsanto Plastic &Resins Co., St. Louis, Mo.

(III) 0.0005% by weight of trifluoro methane-sulfonic acid having a pHof 4 to 6.5.

To this mixture is added the following ingredients.

(I) 25% by weight of silver having a particle size of 2 to 12 microns,an apparent density of 21.5 to 23.5 g/in³, a tap density of 1.5 to 2.5g/in³ and a weight loss at 1000° F. of approximately 1%.

(II) 70.0% by weight of nickel powder which is about 100% spherical,having an average particle size of 12 microns and an apparent density of56.8% g/in³.

This mixture is stirred at room temperature until completely homogenizedand then put through a three roll mill for two passes with the backroller at 4 to 6 mil and the front roller at 1 to 3 mil. The ink wasthen printed by pad 60.

The device is then dried in a convection oven at 200^(F) for 5 minutes.The printed pattern is then pressed with a die at a pressure of 1800p.s.i. for 15 seconds at 450° F. to improve wire bonding properties.

After resilient pad printing by the transfer means, drying and pressingthe thermoplastic of the adhesive and binder are cured to causeinteraction at 360° F. for 30 minutes. The chip carrier device with thecured printed ink adhesively bound to the substrate is thenelectrolessly plated by dipping it in a bath of Enthone Ni418manufactured by Enthone, Inc. of West Hartford, Conn. for 45 minutes at88° C. This forms a nickel plating over the ink which is highlyconductive having a surface resistivity of less than 0.5 ohms persquare.

After plating to the desired plating thickness as for example after 45minutes, a post cure is carried out for 30 minutes at 36° F.

The product produced by this example passes the Platability StandardTest and the Tensile Pull Strength Test of this invention and has anelectrical conductivity such that surface resistivity is no more than0.5 ohms per square.

Example 2

Example 1 is repeated except that in place of the two part adhesivecomposition noted, the following adhesive was substituted:

    ______________________________________                                                           Percents by Weight                                         Solids                   Wet       Dry                                        ______________________________________                                         15%   Formvar 5/95 a    77.14     11.50                                             polyvinylformal                                                               resin obtained from                                                           Monsanto Plastics and                                                         Resins Co., St. Louis,                                                        Missouri in (4/1)                                                             DBE, i.e. of the                                                              dibasic ester:                                                                N--methyl-2-pyrrolidine                                                       mixture of Example 1                                                          (11) as used in the                                                           ink described                                                           40%   of a phenol blocked                                                                             17.35     6.94                                              toluene dissocyanate                                                          in cellosolve acetate                                                         Mondur S in CA                                                                obtained from Mobay                                                           Chemical Co.                                                           100%   of the allyl ether                                                                              1.15      1.15                                              of a phenol formal-                                                           dehyde resin                                                                  Methylon 75108                                                                obtained from                                                                 General                                                                       Electric Co.                                                           100%   of hexamethyl     0.86      0.86                                              ester of hexa-                                                                methyl melamine                                                               Cymel 303 obtained                                                            from American                                                                 Cyanamid                                                               100%   FC 430, a fluoro- 1.15      1.15                                              carbon non ionic                                                              surfactant obtained                                                           from Minnesota                                                                Mining and Mfg. Co.                                                           of Minneapolis, MN                                                            4/1 of the dibasic                                                                              2.89                                                        ester:                                                                        N--methyl-2-pyrrolidine                                                       mixture of Example 1 (11)                                                     as used in the ink                                                            described                                                              ______________________________________                                    

The chip carriers produced by the method of this invention haveexcellent electrical and mechanical characteristics.

Example 3

Example 2 is repeated except that the metal component carrying ink ofExample 1 is replaced by the following formulation.

    ______________________________________                                                           Percents by Weight                                         Solids                   Wet       Dry                                        ______________________________________                                         15%   Formvar 5/95 in (4/1)                                                                           13.20     1.98                                              DBE/N--Methyl-2-                                                              pyrrolidone                                                            100%   Epoxy Novolac Resin                                                                             3.00      3.00                                              used in the ink of                                                            Example 1 (I)                                                                 D.E.N. 431                                                                    A low aspect ratio nickel                                                                       95.00     95.00                                             particle of 3-5 micron                                                        particle size (Inco                                                           123 obtained from                                                             Novamet of                                                                    Wyckoff, N. J.                                                                (4/1) DBE/N--Methyl-2-                                                                          10.73     --                                                pyrrolidone                                                                                     121.93    99.98                                      ______________________________________                                         Total solids = 82.00%                                                         Viscosity = 390,000 cps ± 20,000 (Brookfield viscometer, spindle speed     2) at 29° C.                                                           Sp. Gr. = 6.75                                                           

Example 4

Example 3 is repeated except that the ink formulation used is asfollows:

    ______________________________________                                                           Percents by Weight                                         Solids                   Wet       Dry                                        ______________________________________                                         15%   Formvar 5/95 in (4/1)                                                                            13.20    1.98                                              DBE/N--Methyl-2-                                                              pyrrolidone =                                                          100%   Epoxy Novolac Resin                                                                             3.00      3.00                                              D.E.N. 431 =                                                           100%   FC 430 =          1.00      1.00                                              Fe.sub.2 P HRS 2132,                                                                            66.16     66.16                                             a product of Hooker                                                           Chemical Co. of                                                               Niagara Falls, NY                                                             (3 micron) particles =                                                        (4/1) DBE/N--      4.60                                                       Methyl-2-pyrrolidone =                                                                          87.96     72.14                                      ______________________________________                                         Total solids = 82.00%                                                         Viscosity = 390,000 cps ± 20,000 (Brookfield viscometer, spindle 7,        speed 2) at 29° C.                                                     Sp. Gr. = 4.77                                                           

In addition a surface activation of the printing ink was carried outjust prior to the plating step used. In the surface activation step,palladium chloride solution formulated as follows was used:

1000 Ml deionized water

10 ml concentrated hydrochloride acid reagent grade

0.5 gram powdered palladium chloride

mix well in agitator for one hour to uniformly dissolve.

The chip carrier was dipped into the palladium chloride solution for oneminute at room temperature. After rinsing with water, the chip carrierwas then plated as previously done in Example 1.

Example 5

Example is repeated except that the ink formulation used is as follows:

    ______________________________________                                                           Percents by Weight                                         Solids                   Wet       Dry                                        ______________________________________                                         15%   Formvar 5/95 in (4/1)                                                                            13.20    1.98                                              DBE/N--Methyl-2-                                                              pyrrolidone =                                                          100%   Epoxy Novolac Resin                                                                             3.00      3.00                                              D.E.N. 431 of Example 1 =                                              100%   FC 430 =          1.00      1.00                                              Fe.sub.2 P HRS 2132                                                                             8.00      8.00                                              (5 microns) =                                                                 Micro 470 graphite                                                                              8.00      8.00                                              (1 micron) obtained                                                           from Asbury Graphite                                                          Mills, Inc., Asbury,                                                          New Jersey =                                                                  Fluorocarbon powders                                                                            8.00      8.00                                              (FLUO HTG-2)                                                                  (lubricant) obtained                                                          from Micro Powders,                                                           Inc., of Yonkers, NY =                                                        (4/1) DBE/N--      --                                                         Methyl-2-pyrrolidone =                                                                          41.20     29.98                                      ______________________________________                                         Total solids = 72.88%                                                         Viscosity = 340,000 cps ± 20,000 (Brookfield viscometer, spindle 7,        speed 2) at 29° C.                                                     Sp. Gr. = 2.24                                                           

In addition a surface activation of the printing ink was carried out asin Example 4.

Example 6

Example 5 is repeated except that the adhesive is replaced with thefollowing adhesive formulation:

    ______________________________________                                                           Percents by Weight                                         Solids                   Wet       Dry                                        ______________________________________                                        18%     Formvar 5/95 in (4/1)                                                                           55.56    10.00                                              DBE/N--Methyl-2-                                                              pyrrolidone =                                                         60%     Mondur S in      10.00     6.00                                               Cellosolve                                                                    Acetate =                                                             100%    Methylon 75108 = 1.00      1.00                                       100%    Cymel 303 =      0.75      0.75                                       10%     Paint Additive 11                                                                              0.50      0.05                                               a silicone surfactant                                                         obtained from Dow                                                             Corning Co. of                                                                Midland, Michigan =                                                           (4/1) DBE/N--     14.50                                                       Methyl-2-pyrrolidone =                                                                         32.31     17.80                                      ______________________________________                                    

Example 7

Example 1 is repeated except that the Rynite 555 substrate is replacedwith 35 parts by weight Polyarylethersulfone, 35 parts by weight ofpoly(ethylene terephthalate) (Cleartuf 7202A, obtained from GoodyearTire and Rubber Co.), 20 parts by weight of fiberglass (OCF-497B,Owens-Corning Corp., Anderson, S.C. and 10 parts by weight of talc(reagent grade, Mallinckrodt, Inc., Paris, Ky. were blended in a singlescrew one-inch diameter extruder (L/D=20) equipped with a Maddox mixinghead at about 275° C. and molded into chip carrier substrates of theform described in example 1.

The polyarylethersulfone used is a polymer having the following repeatunit: ##STR1##

The polymer has a reduced viscosity of 0.61 dl/g as measured inN-methyl-pyrrolidinone (0.2 g/100 ml) at 25° C.

Example 8

The material in example 7 is replaced with 35 parts by weight ofPolysulfone, 35 parts by weight of the poly(ethylene terephthalate) ofExample 7, 20 parts by weight of fiberglass (OCF-497B, Owens-CorningCorp., Anderson, S.C.) and 10 parts by weight of talc (reagent grade,Mallinckrodt, Paris, Ky. These materials are processed in accordancewith the method of examples 1 and 7.

The polymer has the following repeat unit: ##STR2## This polymer has areduced viscosity of 0.47 dl/g as measured in chloroform (0.1 g/100 ml)at 25° C.

In all of the above examples, the platings obtained in the chip carriersare extremely useful. In the case of the nickel and the silver-nickelcombinations, the devices formed pass the Plateability Standard Test andthe Tensile Pull Test of this invention. In all cases, the novel andadvantageous three-dimensional printing step enables formation ofthree-dimensional devices without later forming to form qualitycomponents with good resolution, good electrically conductive propertiesand good bonding properties.

While specific examples of this invention have been described and shown,it should be understood by those skilled in the art that many variationsare possible. The novel printing step, inks, plating and printingsequence and the like along with the interaction materials are among theunique aspects of this invention. It should be understood that althougha specific adhesive layer is preferably used, in some cases thesubstrate on which the ink is to be printed may itself be in a form suchthat is has an adhesive outer surface avoiding the need for a separateadhesive.

What is claimed is:
 1. A three-dimensional device comprising athermoplastic or thermosetting, or mixtures thereof, organic resinsubstantially rigid substrate having a thickness and defining a firstside surface comprising an electronic component mounting area, a flangeextending at an angle from the mounting area and defining a lip areahaving an outer peripheral edge,a particle-loaded ink lying in aplurality of distinct circuit paths and extending from the vicinity ofsaid mounting area toward said lip, said particle of said ink comprisinga metallic component, said particle-loaded ink being bound to saidsubstrate by a curable cross-linkable thermosetting organic resin, and aconductive metal plating plated over said ink, said device having acoefficient of thermal expansion predetermined to match closely withthat of an organic resin printed circuit board.
 2. A three dimensionaldevice in accordance with claim 1 in the form of an electronic chipcarrier wherein,said ink has an underlying layer of a thermosettingresin adhesive and an ink binder of a compatible thermosetting organicresin, said particle of said ink comprising a metallic component.
 3. Athree-dimensional device in accordance with claim 2 wherein saidparticle is in the form of a plurality of particles selected from thegroup of particles consisting of precious metals such as least one ofsilver, gold, platimum, palladium, rhodium and ruthenium, mixtures ofprecious metals and non-precious metals such as nickel, non-preciousmetals such as nickel alone and metal-containing materials such as Fe₂P.
 4. A three-dimensional device in accordance with claim 2 wherein saidcircuit path extends over said surface from the vicinity of saidmounting area along the angle of said flange and over said lip to saidouter peripheral edge to provide a good fileted solder bond with acircuit board to which the device is soldered.
 5. A three-dimensionaldevice in accordance with claim 4 wherein said chip carrier has an outerparameter within the scope of a 0.4" to 2.5" square.
 6. Athree-dimensional device in accordance with claim 5 wherein said ink isprinted on a substrate by a yieldable printing means capable ofconforming to a three-dimensional surface to provide good resolution andfine lines of conductive path on said substrate,and said device meetsthe Plateability Standard Test and the Tensile Pull Strength Test.
 7. Athree-dimensional device comprising an organic resin substrate inaccordance with claim 6 wherein said ink is bound to said substrate by acured resin and said ink comprises a thermosetting resin binder suchthat the cured resin and binder resin are capable of functionallyreacting.
 8. A three-dimensional device in accordance with claims 1, 2or 6 wherein ink is compacted prior to applying said plating to providea smooth surface on said plating suitable for wire bonding.
 9. Athree-dimensional device in accordance with the device of claim 2 incombination with a printed circuit board having conductive paths adaptedto coincide with said three-dimensional device conductive paths,saidconductive paths of said circuit board and three-dimensional devicesbeing in registration and solder bonded to each other to provide anenclosed housing for an electronic device mounted on said mounting area.10. A combination in accordance with claim 9 wherein said solder bondingextends to a portion of said conductive path of said three-dimensionaldevice which portion extends over said peripheral edge thereby providinga fileted seal and solder bond to said circuit board.
 11. Athree-dimensional device in accordance with claim 2 wherein said organicresin has a moisture absorption of below 0.05%.
 12. In an electricallyconductive device having an electrically insulating substrate, theimprovement comprisinga circuit pattern comprising a deposited layer ofFe₂ P particles and an electrically conductive layer plated thereover.